Metallic film diffusion for boundary lubrication



1 r 2 3,391,080 l face with the metal thereon, allowing the surface to cool f ...,.,andwiping the excess metal therefrom. Subsequently,v a BOUNDARY post-heat treatment is given wherein the surface with the ,DGHaIdHH. Buckley, North Robert L. Join metallic thereon is reheated and allowed t C001 t0 summit-view Park, onto. as' s ignorstothe United States 5 room temperature thereby lmprovmg t tncuon n l iofAmerica as represented by the Administratorofithe- 'P P of the Surface With the metallic National Aeronautics and Space Administration Other objects and advantages of the present invention N0 Drawing. Original applica i n Oct- 1 1963, serigNo- 1' (will be described and will be apparent from the following f N iv s r y description and the several embodiments thereof. Divided and this application Nov. 15, 1966, Ser. No.

594 633 10 The surface upon which the lubricant film of the present p 7 Claims. (Cl invention is robe applied is ,cleaned Thisis accomplished v g j v i 1 by, rinsing the-surface with acetone orauothersolventito remove grease and oi1..;. Subsequ ently, the surface is polished with moist levigated aluminum or othersimilar ABSTRACT 5 grinding compounds with a soft cloth...This polishing con- Galliuinditfused intoa surface forms a metallic; tinuesuntil the surface is perfectly-clean. lubricant. Tin, lead,l. andindiu m areadded tothe gallium .After polishingthe. surface and thereby improving to a tofreduce corrosion properties vand." loi le liquid .p ase degree-the-surface finish, thesurface is thoroughly .Ii SQ temperatures. a. Q with tap-water followed 'by distilled water. The-rinsing v 3 I u p 2 process can also be accomplished with alcohol or another 1 55S similartype offluid. #32:.a ggg g gfsg ggs i ggg$2333 g h f z After cleaning the surface to which the lubricating film tufed usedby for flu Government. {on govern, s to be appl1ed, the metal which 18 to comprise the lubrimental purposes without the payment of any royalties ca app edt e i rfaceata temperature above thereon or therefon which it is in a liquid state. The hquified metal-1s appl ed The invention relates geiierallystdmetallic film lubrit the Surface hyameahs of ahhpphpatqhwhtch, depend cants. More particularly," the'invention is concerned with t g upon the 13 and/Or the tempetathre of the thetah a metallic film which'is diffused into a metal or other h he Pohshthg cloth' The metal 15 thhhhd over ahd material for use as alubricanh (infused into the surface by applymg a sufficient amount This application is adivisionT-of copendng application htiprehshrefo the apphcator- Where the ttrmphrathhe 0t Ser. No. 316,477 which-wasfiled'Oct. 15, 1963 and issued th metal 15 beyondfihat Whwh can be handledwa as us p 3317,3415; v v human hand, the applicator can be of a soft heat res stant ln=aerospace applications .-where highneliability is ide h h t not rhactive t the F metal s h sirable, it becomes necessary for moving parts to=operate to h Shh-face hPoh whtch the htlthd metal 15 t h over substantialtemperature ranges in thewacuum of outer hP 1 space Difficulty .is; experiencedwith ava-ilableoil and After the hqthd thetal ts hhlfomhy chsmbhted over h grease lubricants because oftheir highevaporation'rates. hh theosample 1S h h 'E a f h f 9 PPF Some inorganic solid an d-soft-l-materials having tveryalow mathly 100 hhove hhtlal hqhld P a temperathhe eva oration ratesin vacuum-ea pearsto have: romise as t? h thehqhthed thetat to cohtpletetyhoat t h h h 'b g f lubricants fen spacetgvhere suchilubllicantsyal-e 40 and diffuse into the matenalsurface. The sample. s then used as a liquid or in dispersed powderrform; problems of lew P to Its -F q d phase-thmperathre and zero gravity prohibit adequate lubrication asrthe lubricant .i t h dry w a Y l h to hemove ,hh ch55 w m maintain itself Withimtheqnvimnmemof thaw? metal. It has been found that this method will form a faceto be lubricated. Consequently; alubri-cationsystemis 1 9 metahh? fi hohhhary thhhcaht on a surface used whereby a; solid film lubricantisformed on asurfaee phoxhhatety-o'ool lhch to be lubricated which would act as a boundary lubricant. It has hh hhthehtohhd thhtfohmhst hhhsa P However where metallicfilm lubricants are required, h treatmeht 1S preterahle' T Post'heat treatmeht. h difficulty is experinc din'a pply them to material sur- 5 h h plhclhg the surface h h methhh? film thereoh faces used in aerospaceenvironments-The main difiiculty h ahhhclosed choamher h hh to h t of is that these metallicfilms will not maintain themselves approhlmhtely 0 above us thmal hqhldhhash on the surface to be lubricated after application. Further, h th for a h d approxlmhtely one hour In a the conditions of enter s'p ac dititate high operating temmethod for accomphshthg the athreshld, a vacuum fut-nah:

can be used to eliminate oxidation problems. The surface peratures due to solar; radiation and heat, generation experienced from rocket engine combustion. TherefQre, .-it i h' the lubricant thereon 1S ltheh removed from the is also necessary .t onhave lubricant: films which will.-be r h h and is allowed to cool to room temperathr? h resistant to temperatures to 0 6 3 I j L post-heat treatment temperature and the length of time in Accordingly, anobject of theinventionlis t provide furnace can h .vaned; hccordlhgly".mls vat-1am? metallic films to be applied to rnetaliceramie' and cermet :vohld h g hig g wear pthperhes Qt thhshr surfaces which canbe used'ras boundary.lubricantsinan aces asso-cla 6 W1 aerospace environment. t I I I i h} .r' i the hhoresald method 9 the P h Another object of this'inventionfis.to -proilidea as t it e poseble lmpregnate mammals e {metal Winch with 'surfaces of a metallic film ditfused thereinnas I :hhretofore could not be done wherem the lmpreghated tinguished from a mere coating of arrietallic film it metals would form a film oh the Surfaces and act as h V a t "boundary lubricant. I I ahhthehvohlect a rhh. ht h 9. Pl' For space applications, it is Preferable that materials hii h g hmhhhhhs 1 selected for a boundary lubricant have a low shear rate to W an s h emphrhhtestofl hd'hhye'h give low friction coefiicients, have as low a melting. or low evaporation rate. i i i x liquid phase temperature aspos'sible, and have a, low evap- B hyi hese and "o Objects"oflvthei-lnveh'holl'ahe oration rate. Further, the film should haveas. lowan attained preparingthersurfacevto .h -1ubrioated, rubbing oxidation rate as possible. A metal which can be used with thereon l quified metals-such as gall um and galhumtdrl 'th'e method-'ofthe present invention is gallium. flin, lead comblnaflon W131 i111, indium jandleads lh6'at1ng the" Sl1I Y and indium can be added to the gallium in various amounts to provide for metallic film lubricants h aving reduced I possible. For gallium at normal atmospheric conditions,

corrosion properties and, in'some instances, a lower liquid phase temperature.

the"followin'gcan'beachieved by the additionof tin or indium to the gallium.

TABLE 1 Pressure 4400 Stainless Steel 011 A1203 on 4400 Stainless 440C Stainless Steel Steel Air, 29.9 mm. of mercury Vacuum, mm. of mercury.

The following examples describe in greater detail the metallic film lubricants and the procedure for applying to a surface the aforesaid metals for use as a metallic film for boundary lubrication:

As a first'example, gallium is used as the metallic film lubricant. Gallium is in liquid form over a temperature range of more than 3500 FQAt atmospheric pressures, the liquid range is from approximately 86 F. to 3600 F. Gallium also has a low evaporation rate, that being 1X10 grams/cm. sec. While the gallium in actual application is applied to the surface of face seals which are made out of metals and ceramics, such as tool steels and alumina, or to bearing cages made out of graphite, lead and titanium, for the purposes of this example the gallium as well as the other metals were applied to a fiat disc surface made out of 440C stainless steel which can be used in conjunction with a rider for friction and wear measurements.

As previously described, the disc specimen is prepared by rinsing with acetone to remove greases, oils and other contaminants contained thereon. Subsequently, the disc is polished with levigated alumina on a soft cloth and thoroughly rinsed with tap water followed by distilled water. Subsequently, liquid gallium is applied under pressure to the surface by means of a soft polishing cloth applicator in order to uniformly distribute the gallium over and into the surface of the disc. The aforesaid was accomplished at the lower liquid phase temperature of the gallium which is approximately 86 F. The disc with the gallium contained thereon and diffused therein is heated to a temperature of approximately 200 F. to allow the gallium to more completely coat and dilfuse into the surface of the disc. The sample is subsequently wiped with a dry cloth to remove excess gallium immediately after heating. Subsequently, the sample is allowed to cool forming a film of approximately 0.001 inch thick on the surface of the disc.

The disc with the gallium film is given an additional treatment consisting of placing the disc specimen with the metallic film into a vacuum furnace and heating the disc to 500 F. for a period of approximately one hour. The disc is then removed from the furnace and allowed to cool to room temperature.

It has been found that for gallium where the time of the post-heat treatment was substantially less than one hour and at temperatures substantially lower than 500 F. the friction and wear for the disc-film combination was higher." Whereas, when the post-heat treatment temperature was I000 F., the friction and wear properties were the same as for 500 F. Consequently, in the present embodiment of the invention, optimal friction and wear results were obtained with a post-heat temperature between 450 F. and 550 F. for an approximate period of one hour.

The following table is an example of friction and wear properties of the gallium as a metallic surface film according to the present invention using two material combinations under atmospheric conditions and in a vacuum.

In use of any type of metallic film applied to a surface as herein described, it is preferable that the metal used for the film have as low an initial liq id phase temp as As a second example of the present invention, approximately 8 percent tin is added to gallium which lowers the initial liquid phase temperature of the pure gallium from approximately 86 F. to 68 F. This facilitates the application of the metallic film lubricant. Using 92 percent by weight gallium and 8 percent by weight tin, the eutectic alloy is applied as heretofore described for gallium ,in Example 1; however, the application temperature is at room temperature that being approximately 72 F.

The following additional eutectic alloys of tin-gallium are found to provide adequate boundary lubrication to temperatures beyond 1000 F. and have an initial liquid phase temperature below that of pure gallium.

Percent Weight Gallium Tin The tin-gallium eutectic alloys give approximately the same friction and wear properties as the pure gallium film in Table l.

As a third example, approximately 24.5 percent by weight indium is added to the gallium whichproduces an initial liquid phase temperature of approximately 60 F. giving the additional advantage of applying this eutectic alloy at a lower temperature than that of pure gallium. The indium-gallium eutectic alloy is applied as in Example 2 for the tin-gallium eutectic alloy.

The following additional eutectic alloys of indiumgallium are found to provide adequate boundary lubrication to temperatures beyond 1000 F. and have an iniitial liquid phase temperature below that of pure gallium.

Percent Weight Gallium Indlum The indium-gallium metallic surface films produce friction and wear results which do not vary significantly from that presented for the gallium metallic film lubricant summarized in Table 1.

In many instances, pure gallium will be corrosive to certain materials. Over a period of time, such corrosion will occur in apparently inert materials such as stainless steel. Tin, indium and lead added to the gallium in various amounts reduces the corrosivity of the gallium with various materials.

As a fourth'example, lead is added to the gallium in various amounts from 5 percent to 50 percent. The addition of lead to gallium will not reduce its liquid phase temperature. The corrosivity of the alloy can, however, be reduced. Friction and wear tests for the gallium-lead alloy with amounts of lead by percent weight contained therein, up to 50 percent, indicated that the friction and wear properties of this alloy did not vary significantly from that of pure gallium alone. i

In an embodiment of the present invention, a metallic lubricant film can be formed on the contacting surfaces of rotating machinery such as gears, elements of rollingcontact bearings and rotating face seals. A further embodiment of the present invention can be the formation of an intermediate metallic film between two heat transfer surfaces in contact whereby the contact of the surfaces is not on the asperities of the surfaces but rather, the contact is over the entire area as defined by the metallic film.

The present invention and specific embodiments thereto provide not only for metallic film boundary lubricants to and beyond 1000 F., but also lubricants having low friction coefficients and low evaporation rates in aerospace applications.

It is apparent from the above description that various modifications in the specific materials and procedures de scribed may be made within the scope of the invention. Therefore, the invention is not intended to be limited to the particular materials and procedures described in detail herein except as may be required by the appended claims.

What is claimed is:

1. A metallic film boundary lubricant having an initial liquid phase temperature below 100 F. comprising a eutectic alloy of gallium and a corrosion reducing metal having a melting point under 1000 F. selected from the group consisting of lead, indium, and tin.

2. A metallic film boundary lubricant as claimed in 6 claim 1 consisting of a eutectic alloy of gallium and ead.

3. A metallic film boundary lubricant as claimed in claim 2 comprising a binary alloy of gallium and between about 5 percent and about 50 percent by weight lead.

4. A metallic film boundary lubricant as claimed in claim 1 consisting of a eutectic alloy of gallium and indium.

5. A metallic film boundary lubricant as claimed in claim 4 comprising a binary alloy of gallium and indiu-m between about 12.5 percent and about 71 percent by weight indium.

6. A metallic film boundary lubricant as claimed in claim 1 consisting of a eutectic alloy of gallium and tin.

7. A metallic film boundary lubricant as claimed in claim 6 comprising a binary alloy of gallium and between about 4 percent and about percent by weight tin.

References Cited UNITED STATES PATENTS 2,700,623 1/1955 Hall 11771 2,980,475 4/1961 Wolfe 252-25 3,141,238 7/1964 Harman 29498 DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner, 

